Device and method to discriminate between supraventricular tachycardias and ventricular arrhythmias

ABSTRACT

This invention provides a method to discriminate between ventricular arrhythmia and supraventricular tachycardia by detecting an earliest arriving electrical signal following antitachycardia pacing. Also disclosed is an implantable cardiac defibrillator that is capable of simultaneous atrioventricular anti-tachycardia pacing bursts and detecting an earliest arriving electrical signal. The discrimination capability reduces the incidence of inappropriate shocks from dual-chamber implantable cardiac defibrillators to near zero and provides a method to differentially diagnose supraventricular tachycardia from ventricular tachycardia.

FIELD OF THE INVENTION

This invention relates to the identification and detection of abnormalheart rhythm occurring in either the supraventricular or ventricularcardiac regions. Specifically, this invention relates to a novel methodof analysis to discriminate between supraventricular tachycardia andventricular arrhythmia More specifically, this invention relates to animplantable cardiac defibrillator device controlled by a novel method ofanalysis to discriminate between supraventricular tachycardia andventricular arrhythmia.

BACKGROUND

Identifying the mechanism of an arrhythmia based on its intracardiacelectrograms has become a common challenge to both implantable cardiacdefibrillators (ICDs) and the physicians taking care of patients withICDs. These devices, which are primarily designed to deliver therapy forlife-threatening ventricular arrhythmia, frequently deliverinappropriate shocks for supraventricular tachycardias. Theseinappropriate shocks constitute a significant source of physical andemotional distress for patients, cause early ICD battery depletions, andgenerate a huge financial burden on the health system.

Inappropriate electroshocks from implanted cardiac defibrillatorsconstitute a significant source of physical and emotional distress onthe patients and an unnecessary expense for the health system. Earlygenerations of implantable cardiac defibrillators operated with anincidence of inappropriate electroshocks as high as 20 to 40%. TanakaS., An Overview Of Fifth-Generation Implantable CardioverterDefibrillator, Ann Thorac Cardiovasc Surg., 4:303-311 (1998). Followingthe introduction of dual-chamber implantable cardiac defibrillators,however, the overall success for delivering appropriate electroshocksincreased to 86-100%, while the successful incidence for the treatmentof ventricular arrhythmias reached 97-100%.

The incidence of inappropriate electroshocks in response tosupraventricular tachycardias, however, remains a problem. This problemis especially severe for discriminating between supraventriculartachycardias having 1:1 antegrade conduction and ventricular arrhythmiashaving 1:1 retrograde conduction. Thompson et al., VentriculoatrialConduction Metrics For Classification Of Ventricular Tachycardia With1:1 Retrograde Conduction In Dual-Chamber Sensing ImplantableCardioverter Defibrillators, J Electrocardiol., 31:152-156 (1988)

In an attempt to solve this problem, those skilled in the art haveattempted using various mathematical algorithms to utilize thequantitative aspects of the ECG with variable success. Specifically, themorphology of a shocking electrogram may be compared to a sinus beattemplate. Gold et al., A New Defibrillator Discrimination AlgorithmUtilizing Electrogram Morphology Analysis, Pacing Clin Electrophysiol.1999;22:179-182 (1999) Additionally, stability criteria may be employedto distinguish between atrial fibrillation and ventricular arrhythmiaBarold et al., Prospective Evaluation Of New And Old Criteria ToDiscriminate Between Supraventricular And Ventricular Tachycardia InImplantable Defibrillators, Pacing Clin Electrophysiol., 21:1347-1355(1998); and Schaumann et al., Enhanced Detection Criteria In ImplantableCardioverter-Defibrillator To Avoid Inappropriate Therapy, Am JCardiol., 78:42-50 (1996). In comparison, discrimination between sinustachycardia and ventricular arrhythmia may be determined by theemployment of sudden onset criteria. These approaches have reduced therate of inappropriate electroshocks, but continue to remain atapproximately 11%. Schaumann et al. (supra).

The ability to reduce or avoid all inappropriate electroshocks fromimplantable cardiac defibrillators would have a beneficial effect on thephysical and emotional state of patients with defibrillators as well asreduce the cost of health care. Clearly, what is needed in the art is amethod and a device to prevent the misinterpretation of cardiacelectrical signals and avoid the delivery of inappropriateelectroshocks.

SUMMARY

This invention relates to the identification and detection of abnormalheart rhythm occurring in either the supraventricular or ventricularcardiac regions. In one embodiment, the present invention contemplates anovel method of analysis to discriminate between supraventriculartachycardia and ventricular arrhythmia In another embodiment, thepresent invention contemplates a new implantable cardiac defibrillatordevice controlled by a novel method of analysis that discriminatesbetween supraventricular tachycardia and ventricular arrhythmia.

The present invention contemplates a novel capability that detects anearliest arriving electrical signal (i.e., an intracardic electrogram)that discriminates between supraventricular tachycardia (SVT) andventricular tachycardia (VT). This technique is based on intracardiacelectrograms (EGMs) recorded by atrial and ventricular sensing leadsthat distinguish their temporal relationships following tachycardiarecurrence subsequent to a train of simultaneous anti-tachycardia pacing(ATP) bursts in the atria and ventricles.

One aspect of the present invention contemplates a device, comprising:a) a implantable pacemaker element; b) a implantable defibrillatorelement connected to said pacemaker element; and c) a plurality ofatrial and ventricular pacing leads connected to said pacemaker element,wherein said pacing leads are configured for simultaneous activation. Inone embodiment, the device further comprises a plurality of atrial andventricular defibrillation leads connected to said defibrillatorelement. In another embodiment, the device further comprises a pluralityof atrial and ventricular sensing leads connected to said pacemakerelement. In yet another embodiment, the pacemaker element furthercomprises a storage memory connected to said sensing leads. In oneembodiment, the device is capable of detecting an earliest arrivingelectrical signal.

Another aspect of the present invention contemplates a method,comprising: a) providing: i) a patient implanted with a device,comprising; 1) an implantable pacemaker element; 2) an implantabledefibrillator element connected to said pacemaker element; and 3) aplurality of atrial and ventricular pacing leads connected to saidpacemaker element, wherein said pacing leads are configured forsimultaneous activation and course to the ventricles and atria, whereinsaid pacemaker is capable of analyzing an electrocardiogram; ii) aplurality of sensing leads connected to said pacemaker coursing to theventricles and atria; iii) a plurality of defibrillation leads connectedto said defibrillator coursing to the ventricles; b) detectingventricular and atrial electrical signals by said sensing leads; c)identifying a cardiac arrhythmia with said device; d) initiating one ormore anti-tachycardia pacing bursts by said pacemaker element, whereinsaid ventricles and atria are simultaneously paced; e) detecting anearliest arriving electrical signal following termination of saidanti-tachycardia pacing burst. In one embodiment, a cardiac arrythmia isdetected in the patient. In one embodiment, the cardiac origin of acardiac arrytmia is determined by said earliest arriving electricalsignal. In one embodiment, the earliest arriving electrical signal isfrom the ventricles. In another embodiment, the earliest arrivingelectrical signal is from the atria. In one embodiment, the methodfurther comprises the step of defibrillating said ventricles underconditions such that normal sinus rhythm is restored.

Another aspect of the present invention contemplates a method,comprising: a) providing; i) a patient; ii) an electrocardiogram array;iii) a plurality of intracardiac quadripole catheters, wherein saidcatheters are configured for simultaneous atrial and ventricular pacing;and iv) a computer configured to receive electrical signals from saidcatheters; b) placing said array on the skin surface of said patient; c)inserting said catheters into said patient; d) simultaneously pacingsaid atria and ventricle; e) detecting with said computer an earliestarriving electrical signal. In one embodiment, the earliest arrivingelectrical signal is from the ventricles. In another embodiment, theearliest arriving electrical signal is from the atria. In anotherembodiment, the earliest arriving electrical signal is from the junctionbetween the ventricles and atria. In one embodiment, the method furthercomprises the step of diagnosing said patient as having ventriculartachycardia. In another embodiment, the method further comprises thestep of diagnosing said patient as having supraventricular tachycardia.In yet another embodiment, the method further comprises the step ofdiagnosing said patient as having atrioventricular nodal reentranttachycardia. In one embodiment, said computer is connected to a datareadout device.

In a further aspect the present invention contemplates a method todetect the origin of a cardia arrythmia, comprising: a) providing; i) apatient exhibiting cardiac arrhythmia; ii) an array comprising sensingleads; iii) a computer connected to said array; and iv) pacing leadsconnected to said computer; b) simultaneously pacing the atria andventricles with said pacing leads of said patient under conditions suchthat said patient atrial and ventricular activity is synchronized; andc) sensing with said sensing leads said atrial and ventricularelectrical activity after said pacing under conditions such that theearliest arriving electrical activity is detected.

Another aspect of the present invention contemplates a method,comprising: a) providing: i) a patient implanted with a device,comprising; 1) an implantable pacemaker element; and 2) a plurality ofatrial and ventricular pacing leads connected to said pacemaker element,wherein said pacing leads are configured for simultaneous activation andcoursing to the ventricles and atria; and ii) a plurality of sensingleads connected to said pacemaker coursing to the ventricles and atria;b) initiating one or more pacing bursts by said pacemaker element,wherein said ventricles and atria are simultaneously paced; and c)detecting an earliest arriving electrical signal following terminationof said pacing bursts. In one embodiment, prior to step b), a cardiacarrythmia is detected in said patient. In one embodiment, said earliestarriving electrical signal is from the ventricles. In anotherembodiment, said earliest arriving electrical signal is from the atria.In one embodiment, the method further comprises step d) defibrillatingsaid ventricles under conditions such that normal sinus rhythm isrestored.

Another aspect of the present invention contemplates a method,comprising: a) providing; i) a patient; ii) an electrocardiogram array;iii) a plurality of intracardiac quadripole catheters, wherein saidcatheters are configured for simultaneous atrial and ventricular pacing;and iv) a computer configured to receive electrical signals from saidcatheters; b) placing said array on the skin surface of said patient; c)inserting said catheters into said patient; d) simultaneously pacingsaid atria and ventricles; and e) detecting with said computer anearliest arriving electrical signal. In one embodiment, the earliestarriving electrical signal is from the ventricles. In anotherembodiment, the earliest arriving electrical signal is from the atria.In yet another embodiment, the earliest arriving electrical signal isfrom the junction between the atria and ventricles. In one embodiment,the method further comprising the step of diagnosing said patient ashaving ventricular tachycardia. In another embodiment, the methodfurther comprises the step of diagnosing said patient as havingsupraventricular tachycardia. In yet another embodiment, the furthercomprises the step of diagnosing said patient as having atrioventricularnodal reentrant tachycardia. In one embodiment, the computer isconnected to a data readout device.

Yet another aspect of the present invention contemplates a method todetect the origin of a cardia arrythmia, comprising: a) providing; i) apatient exhibiting cardiac arrhythmia; ii) a system comprising aplurality of pacing leads and a plurality of sensing leads; b)simultaneously pacing the atria and ventricles of said patient; and c)sensing with said sensing leads said atrial and ventricular electricalactivity after said pacing under conditions such that the earliestarriving electrical signal is detected. In one embodiment, the earliestarriving electrical signal is from the ventricles. In anotherembodiment, the earliest arriving electrical signal is from the atria.In yet another embodiment, the earliest arriving electrical signal isfrom the junction between the atria and ventricles. In one embodiment,the method further comprises the step of diagnosing said patient ashaving ventricular tachycardia. In another embodiment, the methodfurther comprises the step of diagnosing said patient as havingsupraventricular tachycardia. In yet another embodiment, the methodfurther comprises the step of diagnosing said patient as havingatrioventricular nodal reentrant tachycardia. In one embodiment, thecomputer is connected to a data readout device.

In U.S. Pat. No. 6,076,014 (herein incorporated by reference), animplantable dual chamber defibrillator capable of dual chamber pacing isdisclosed. This defibrillator is revealed as capable of providingcontinuous atrial pacing or pacing of ventricular chambers as a responseto a detected arrhythmia. The '014 patent does not disclose thesimultaneous pacing of atria and ventricles to diagnose a tachycardiaorigin. Specifically, the '014 disclosure evaluates sensed ECG data by afuzzy logic paradigm that is acknowledged to be imprecise. The fuzzylogic assessment in the '014 patent includes input regarding: i) atrialrates, ii) ventricular rates, iii) ECG morphology, iv) the historicaltrends of ECG data, and v) accelerometer data (i.e., real-timemeasurement of patient movements)

The present application provides a novel method and device when comparedto the '014 patent as well as being simple, specific, accurate. Thedisclosed capability of detecting an earliest arriving electrical signalreliably discriminates between ventricular arrhythmia andsupraventricular tachycardia and objectively provides a defibrillationdecision only for a condition of ventricular arrhythmia. Specifically,this capability relies on the relative arrival times of electricalactivity from either the ventricles or the atria, after synchronizationby simultaneous pacing. The '014 makes no mention of usinganti-tachycardia pacing in combination with a blanking period to assesswhich heart chamber resumes activity first. Instead, the '014 patentrelies on IF-THEN statements that requires information on patientactivity and the relative ventricular and atrial rates.

DEFINITIONS

As used herein, the term “cardiovascular disease” refers to any diseasewhich affects the cardiovascular system including, but not limited to,nerve conduction disorders, thrombophilia, atherosclerosis, anginapectoris, hypertension, arteriosclerosis, myocardial infarction,congestive heart failure, cardiomyopathy, hypertension, arterial andvenous stenosis.

“Symptoms of cardiovascular disease” as used herein refers to anyclinical manifestation of a disease state associated with the heart andthe central or peripheral arterial and venous vasculature. For example,said clinical manifestations include, but are not limited to pain,weakness, high blood pressure, elevated plasma cholesterol, elevatedplasma fatty acids, tachycardia, bradycardia, abnormalelectrocardiogram, external or internal bleeding, headache, dizziness,nausea and vomiting. Thus, a patient suffering from, or exhibitingsymptoms of, cardiovascular disease may detect certain symptoms (i.e.,pain), while other symptoms may not be noticeable to the patient, butare detectable by a health care provider (i.e., elevated bloodpressure).

As used herein, the term “patient” refers to a human or non-humanorganism that is either symptomatic or asymptomatic for cardiovasculardisease. Preferably, a human patient is under the supervision of aphysician or hospitalized.

As used herein the phrase, “patients at risk for cardiovascular disease”refer to patients who have an increased probability, as compared to thegeneral population, of developing some form of cardiovascular disease intheir lifetime. Patients at risk for cardiovascular disease generallyhave one or more risk factors for cardiovascular disease. Risk factorsfor cardiovascular disease include, but are not limited to, a history ofsmoking, a sedentary lifestyle, a family history of cardiovasculardisease, lipid metabolic disorders, diabetes mellitus and obesity.

As used herein, the term “pathophysiological” refers to any condition inan individual or an organ that represents a significant deviation fromestablished homeostatic norms. A pathophysiological alteration is not astructural defect.

As used herein, the term “electrocardiogram” (EKG or ECG) refers to anydisplay of information reflecting changes in heart-tissue membranepotentials in relationship to heart beat. The electrocardiogramcomprises “electrogram activity” (EGM) that refers to any electricalsignal detected by any sensing lead.

As used herein, the term “electrocardiogram array” refers to anyarrangement of skin surface electrodes wherein the integration of thecollected data results in the generation of an electrocardiogram.

As used herein, the term “skin surface” refers to the outer epitheliallayer of a patient.

As used herein, the term “catheter” refers to any device that is usedfor the insertion and placement of electrocardiogram sensing leads intothe intracardial space. Placement of such a device may be inserted into,but is not limited to, the femoral vein, then coursing through the venacava and finally into the right atria and/or ventricle of the patient'sheart.

As used herein, the term “coursing” refers to a path taken through apatient's body by an implanted catheter or electrical leads that may be,but are not limited to, those connected to an implanted ICD, pacemakeror combination thereof.

As used herein, the term “computer” refers to any device capable ofreceiving, storing and calculating data in an electronic format.

As used herein, the term “sinus rhythm” refers to a normal heart beat asquantified by the proper relationships between the P-Q-R-S-Telectrocardiogram segments.

As used herein, the term “arrhythmia” refers to an abnormal heart beatas quantified by improper relationships between the P-Q-R-S-Telectrocardiogram segments. Such arrhythmias may occur during, but arenot limited to, ventricular arrhythmia, supraventricular tachycardia,ventricular fibrillation, atria fibrillation, and bradycardia

As used herein, the term “atrial EGM” refers to electrogram activityfrom electrodes whose sensory input is limited to membrane potentialchanges of the atria. Specifically, these data are collected from, butis not limited to, a high right atrial intracardial electrode placed bycatheterization.

As used herein, the term “ventricular EGM” refers to electrogramactivity from electrodes whose sensory input is limited to membranepotential changes of the ventricles. Specifically, these data arecollected from, but is not limited to, a right ventricular apexintracardiac electrode placed by catheterization.

As used herein, the term “depolarization” refers to the change inmembrane potential that reflects the conduction of an “action potential”which initiates and coordinates the relative contractions of theleft/right atria with the left/right ventricles. Specifically, thesechanges in membrane potential are generated by, but not limited to, thepacemaker cells residing in the right atrium.

As used herein, the term “direction of depolarization” refers to themovement of the electric potential across the heart surface.Specifically, an “antegrade” direction refers to a spreading of thedepolarization from the atria onto the ventricles and subsequent propercoordination of the heart beat. On the other hand, a “retrograde”direction refers to a spreading of the depolarization away from theventricles to the top of the atria and as a result of ventriculararrhythmias.

As used herein, the term “data readout device” refers to any instrumentthat may be connected to a computer that receives and displays theresults of computer calculations. These instruments may be, but are notlimited to, an electronic monitor, a hardcopy printout, and an audiblesignal generated by a computer sound generation program.

As used herein, the term “cardiac defibrillator” refers to any devicethat generates an “electroshock” that is expected to restore normalsinus rhythm in a patient experiencing an abnormal ECG. These devicesmay include, but are not limited to, defibrillators that are safe andeffective when surgically implanted in a patient and auto-activate uponsensing an abnormal ECG. Specifically, these devices may be, but are notlimited to, dual-chamber cardioverter-defibrillators. A “dual-chamber”design is preferred over other cardioverter-defibrillators because theyprovide an ability to simultaneously control the rate of ventricular andatrial contraction and sense their relative electrical activity.

As used herein, the term “inappropriate electroshock” refers to anyelectroshock generated by a cardiac defibrillator that is delivered bymisinterpretation of an ECG. This ECG misinterpretation may occurduring, but is not limited to, sinus tachycardia or othersupraventricular tachycardias.

As used herein, the term “pace” or “pacing” refers to an artificialelectrical stimulation of a heart chamber that supersedes the functionof physiological pacemaker cells. The artificial electrical stimulationmay, but is not limited to, be generated by an electrode within anintracardiac catheter or an ICD.

As used herein, the term “atria” refers to the upper principal cavity ofthe heart auricle (i.e., the sinus venosus) and is situated posteriorlyto the smaller cavity of the auricle, the appendix auricula. The humanheart comprises two atria, one on the left side of the heart and asecond on the right side of the heart. Consequently, the term “atrial”references any matter of, or concerning, either one or both atria.

As used herein, the term “ventricle” refers to the lower, and largest,compartment of the heart. The human heart comprises two ventricles, oneon the left side of the heart and a second on the right side of theheart. Consequently, the term “ventricular” references any matter of, orconcerning, either one or both ventricles.

As used herein, the term “blanking period” refers to any cessation ofelectrogram (EGM) activity from either an atrial or ventricular chamber.A blanking period may be triggered by, but not limited to, ananti-tachycardia pacing (ATP) burst. Specifically, a blanking period isthe shortest period of time, in milliseconds, as measured from the lastATP pacing burst that would include the first captured electrogram (GM)activity from either the atrial and ventricular channels that varies asfunction of tachycardial cycle length. An exemplary calculation of ablanking period might be: (100+TCL)/2 where TCL is the tachycardia cyclelength. The expected duration of a blanking period in a human patient isapproximately, but not limited to, 100-500 msec.

As used herein, the term “anti-tachycardia pacing burst” refers to anytrain of electrical impulses generated from, for example, an implantablecardiac defibrillator or an external signal generator, during an episodeof either supraventricular tachycardia or ventricular arrhythmia thatprovides pacing stimulus to either the atria, ventricles or both.Preferably, the generated signals are of a square-wave morphology. A“simultaneous anti-tacyhcardia pacing burst” refers to any pacingsignals provided to both the atria and ventricle within any 0-40 msectimeframe. Generally, multiple anti-tachycardia pacing bursts aredelivered, wherein each burst has an approximate length of twelve heartbeats.

As used herein, the term “storage memory” refers to any electronic meansthat is capable of retaining digitized information or computer softwareprograms. The digitized information may be binary or complex formulas orequations capable of receiving, and processing, input from atrial orventricular sensing leads.

As used herein, the term “defibrillation leads” refer to any electricalconductive material placed on, or within, a heart chamber that, whenactivated, is capable of converting an abnormal heart rhythm into normalsinus rhythm.

As used herein, the term “sensing leads” refer to any electricalconductive material placed on, or within, a heart chamber that transmitselectrical activity.

As used herein, the term “pacing leads” refer to any electricalconductive material placed on, or within, a heart chamber that, whenactivated, provides an electrical stimulus to control cardiac musclecontractility.

As used herein, the phrase “the capability of detecting an earliestarriving electrical signal” (or analogous phrases) refers to anyelectronic configuration that is capable of discriminating the arrivaltime between at least two electrical signals having a sensitivity ofranging between 0-40 msec. While not intending to limit any embodimentof the present invention, the sensing of atrial EGM or ventricular EGMmay be performed with, or without, calculations based on any formula orequations. For example, EGMs may be filtered by the pacemaker andconnected to a timing device. The output may be, but is not limited to,a binary format. At a minimum, the detection capability answers twoquestions; i) Did the tachycardia terminate? (yes/no), and if it did notterminate, ii) Was the ventricular EGM prior to the atrial EGM?(yes/no).

As used herein, the term “earliest arriving electrogram activity” refersto the first electrical signal detected following a specific timelinemarker (ie., an anti-tachycardia pacing burst).

As used herein, the term “simultaneously arriving electrogram activity”refers to at least two electrical signals detected within a 50-60 msectimeframe.

As used herein, the term “system” refers to any integrated singledevice, or multiple devices connected together, that function in acoordinated manner to produce a desired result. One example illustratedherein, describes a system that detects an earliest arriving electricalsignal comprising integrated single device such as an implantablecardiac defibrillator comprising a pacemaker. Another exampleillustrated herein, describes a system that detects and earliestarriving electrical signal comprising multiple devices connectedtogether such as an electrocardiogram array, a generator (i.e., forexample, pulse or signal) and a computer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cutaway drawing of an exemplary human heart showing theconfiguration of one embodiment of dual chamber implantable cardiacpacer/defibrillator.

FIG. 2 shows a simplified flowchart of data flow and decision points inone embodiment of discriminating ventricular arrhythmia fromsupraventricular tachycardia and initiation of defibrillation.

FIG. 3 shows successful termination of tachycardia in a human patientfollowing 350 msec anti-tachycardia pacing bursts.

FIG. 4A shows ventricular tachycardia persistence in a human patientfollowing 400 msec anti-tachycardia pacing bursts. (blanking period fromlast ATP stimulation to dashed line)

FIG. 4B shows ventricular tachycardia persistence in a human patientfollowing 350 msec anti-tachycardia pacing bursts. (blanking period fromlast ATP stimulation to dashed line)

FIG. 5 shows atrial tachycardia persistence in a human patient following350 msec anti-tachycardia pacing bursts. (blanking period from last ATPstimulation to dashed line)

FIG. 6 shows the presence of atrioventricular nodal reentranttachycardia in a human patient following 360 msec anti-tachycardiapacing bursts. (blanking period from last ATP stimulation to dashedline)

FIG. 7 shows an exemplary normal sinus rhythm tracing in a mouse.

FIG. 8 shows ECG recordings using an octapolar catheter during atrialpacing using a Preva SR pacemaker in a mouse.

FIG. 9 shows ECG recordings using an octapolar catheter duringventricular pacing using a Preva SR pacemaker in a mouse.

FIG. 10 provides an ECG recording using an octapolar catheterillustrating that atrial activity is the earliest electrical activityfollowing an anti-tachycardia pacing burst during a simulatedsupraventricular tachycardia by atrial pacing.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to the real-time identification and detection ofabnormal heart rhythm occurring in either the supraventricular orventricular cardiac regions. Specifically, this invention relates to anovel method of analysis to discriminate between supraventriculartachycardia and ventricular arrhythmia. More specifically, thisinvention relates to an implantable cardiac defibrillator devicecontrolled by a novel method of analysis that discriminates betweensupraventricular tachycardia and ventricular arrhythmia

The clinical manifestations of ventricular arrhythmias range from acomplete absence of symptoms to sudden death. Although the understandingof the pathophysiology and natural history of these arrhythmias hasadvanced significantly over the past decade, large gaps in knowledgeremain, especially in patients with heart failure not due to coronaryartery disease. Many symptomatic ventricular arrhythmias, however, arenow curable using catheters that deliver radio-frequency energy (i.e.,ablation lesioning). It is now clear that the primary treatment forpatients at high risk for life-threatening ventricular arrhythmias isthe implantable cardiac defibrillator.

Determination of atrial tissue depolarization directionality has metwith little success. Various time and frequency domain criteria havebeen mathematically applied to the bipolar atrial electrogram, whichachieve successful discrimination of atrial depolarizationdirectionality in less than 80% of patients. Timmis et al.,Discrimination Of Antegrade From Retrograde Atrial Electrograms ForPhysiological Pacing, PACE 11:130-140 (1988); Wainwright et al., IdealAtrial Lead Positioning To Detect Retrograde Atrial Depolarization ByDigitization And Slope Analysis Of The Atrial Electrogram, PACE7:1152-1158 (1984). Similarly, the use of amplitude and slew ratecriteria resulted in successful discrimination of antegrade versusretrograde atrial depolarization in 81% of patients (McAlister et al.,Atrial Electrogram Analysis: Antegrade Versus Retrograde, PACE11:1703-1707 (1988)). This in contrast to an initial promising studythat could not be reproduced. Pannizo et al., Discrimination OfAntegrade And Retrograde Atrial Depolarization By Electrogram Analysis,Am Heart J. 112:780-786 (1986).

The advent of atrioventricular conduction metrics improved thediscrimination between ventricular arrhythmia and 1:1 supraventriculartachycardia where 80% specificity was coupled with 100% sensitivity whenventriculoatrial times were between 80 and 234 ms. Thompson et al.,Ventriculoatrial Conduction Metrics For Classification Of VentricularTachycardia With 1:1 Retrograde Conduction In Dual-Chamber SensingImplantable Cardioverter Defibrillators, J Electrocardiol., 31:152-156(1988) Beyond these boundaries, both the sensitivity and specificitywere 100%. Similarly, correlational waveform analysis was able todiscriminate between antegrade and retrograde atrial activation, in theabsence of ventricular arrhythmia, during ventricular pacing whenpatient-specific thresholds were adopted and the sampling rate of thesignal was set at 1,000 Hz or greater. Throne et al., Discrimination OfRetrograde From Antegrade Atrial Activation Using IntracardiacElectrogram Waveform Analysis, Pacing Clin Electrophysiol., 12:1622-1630(1989)

The impact of heart rate and sympathetic tone on the shape ofintracardiac ECG waveforms has been assessed. In 36 out of 39 patients,increased heart rates resulting from; i) atrial pacing, ii) epinephrineinfusion, and iii) isoproterenol infusion did not significantly alterECG waveform configuration as assessed by correlation waveform analysis.Finelli et al., Effects Of Increased Heart Rate And Sympathetic Tone OnIntraventricular Electrogram Morphology, Am J Cardiol. 68:1321-1328(1991) In patients with permanent pacemakers, exercise results in a 38%decrease in atrial ECG amplitude without any other morphologic changes.Ross et al., The Effect Of Exercise On The Atrial Electrogram Voltage InYoung Patients, PACE, 14:2092-2097 (1991) The correlation coefficients(p) generated by correlation waveform analysis is independent ofamplitudes and units and should not be adversely impacted by heart rate,sympathetic tone or exercise. Woodroofe M., Probability WithApplications, McGraw-Hill, New York. pp. 229 (1975) It is possible,however, that changes in atrial morphology may occur over time andchanging patient posture. A critical analysis of these variables wouldrequire the use of chronic sensing leads.

Heart Function

The operation of the heart is regulated by electrical signals producedby the heart's sino-atrial (SA) node. Each signal produced by the SAnode spreads across the atria and ventricles of the heart, depolarizingthe muscle fibers as it spreads. Atrial and ventricular contractionsoccur as the signal passes. After contracting, the myocardial cellsrepolarize during a short period of time, returning to their restingstate. Once repolarized, the muscle cells are ready to be depolarizedagain by a signal from the SA node.

At rest, the normal adult SA node produces a signal approximately 60 to85 times a minute, causing the heart muscle to contract, and therebypumping blood to the remainder of the body. This constitutes therepetitive, cyclic behavior of the heart. Each cycle in the operation ofthe heart is called a cardiac cycle.

Atrial geometry, atrial anisotropy, and histopathologic changes in theleft or right atria can, alone or together, form anatomical obstacles.The obstacles can disrupt the normally uniform propagation of electricalimpulses in the atria. These anatomical obstacles (called “conductionblocks”) can cause the electrical impulse to degenerate into severalcircular wavelets that circulate about the obstacles. These wavelets,called “reentry circuits,” disrupt the normally uniform activation ofthe left and right atria. Abnormal, irregular heart rhythm calledarrhythmia, results. This form of arrhythmia is called atrialfibrillation, which is a very prevalent form of arrhythmia.

To analyze the heart's operation, a variety of techniques have beendeveloped for collecting and interpreting data concerning the electricalactivity of the heart. One of the most basic of these approaches is theelectrocardiogram (ECG). As an electrical signal spreads across theheart, an ECG repetitively measures the voltages at various electrodesrelative to a designated “ground” electrode. The ECG typically plotseach lead over an interval of time such that the heart's electricalactivity for one or more cardiac cycles is displayed for purposes ofmonitoring or analysis. The three most common ECG's are known as the “12lead”, the “18 lead,” and the vector cardiograph.

A cardiac cycle as measured by the ECG is partitioned into three mainelements which reflect the electrical and mechanical operation of theheart. The portion of a cardiac cycle representing atrial depolarizationis referred to as a “P-wave.” Depolarization of the ventricular musclefibers is represented by “Q”, “R”, and “S” points of a cardiac cycle.Collectively these “QRS” points are called an “R-wave” or a “QRScomplex.” The portion of a cardiac cycle representing repolarization ofthe ventricular muscle fibers is known as a “T-wave.” It is through theuse of an ECG that one is able to determine whether fibrillation is oris not occurring and allows one to manipulate the heart tissue toprovide treatment.

Pacemakers

A pacemaker maintains the heart rate of a patient between a certainprogrammable range. For example, in humans that range is typicallybetween 60-80 beats per minute (lower rate) and 120-160 beats per minute(upper rate). In one embodiment, the present invention contemplates apacemaker for stimulating the independent conduction zones andreestablishing functional communication between the zones. A pacemakerautomatically applies a pacing impulse to the heart of sufficientmagnitude to depolarize the tissue. The device is adapted to continuedelivering intermittent pacing to the heart in the event that the heartfails to return to its normal behavioral pattern, and has the ability ofautomatically regaining sensing control over a functional heart, therebyinsuring that further pacing is inhibited.

The pacemaker circuit comprises two basic subsystems; a sensing system,which continuously monitors heart activity; and a stimulation systemwhich upon receiving a signal from the sensing system applies a pacingimpulse to the myocardium through an intravascular electrical lead. Afirst bipolar lead may be coupled to the pulse generator and has anelectrode located at its distal end to sense and pace the atrium.Alternatively, the, atrial leads may comprise separate sensing andpacing electrodes. A second bipolar lead coupled to the generator isused for sensing and pacing the ventricle. Alternatively, theventricular leads may comprise separate sensing and pacing electrodes. Acircuit is provided for applying impedance measuring current pulsesbetween one of these electrodes and the others.

In one embodiment, an off-the-shelf pacemaker is capable of both atrialand ventricular pacing/sensing. The specific pacemakers preferred forthis purpose include a Medtronic Sigma, a Medtronic Kappa (both made byMedtronic, Inc. Minneapolis, Minn.), a Guidant Discovery, a GuidantMeridian (both made by Guidant Inc, Minneapolis, Minn.) or PacesetterAffinity (Pacesetter, a St. Jude's company, Minneapolis, Minn.) as thesehave a minimum programmable delay between atrial and ventricular pacingof 10 msec. To effectuate pacing according to one embodiment of theinvention, all leads from the atrial and the ventricular segment of thepacemaker are connected to the atrium and ventricle, respectively. Toallow more than one segment to be paced per lead, a bifurcation systemcan be used. Such leads are commercially available and can be used as anoff-the-shelf product. The Y-adapter (for example CPI MODEL #6835, or#6024, made by Cardiac Pacemakers Inc., Minneapolis, Minn.) would allowone of the sockets from the pacemaker (atrial or ventricular) to then bebifurcated to at least two leads. Therefore, each output would then beable to pace at least two electrically isolated segments. For epicardialpacing, CPI model #4312 lead (Cardiac Pacemakers Inc., Minneapolis,Minn.) can be used and this has a 4.75 mm pin. For endocardial pacing,CPI model #4161 (Cardiac Pacemakers Inc., Minneapolis, Minn.) could beused. In this manner, a standard dual chamber pacemaker could be used topace four intracardial segments.

Sensing Elements of a Pacemaker

In a standard dual chambered pacemaker, the sensing circuits monitoractivity both in the atrium and ventricle. If a sensed event occurs inthe atrium, this initiates a ventricular paced event if no ventricularactivity occurs during the programmed atrio-ventricular delay. If nosensing occurs in the atrium or ventricle, pacing is initiated tomaintain the programmed lower rate.

When the pacemaker device is used for the present invention, similarsensing algorithms will be useful in the appropriate pacing of thevarious intracardiac segments. It is particularly desirable that thepacemaker include a sensor of a physiologic parameter related to demandfor cardiac output, such as an activity sensor, a respiration sensor oran oxygen saturation sensor. Various dual chamber pacing devices haveincorporated some form of sensor to provide a physiologic pacing rate.Similar sensing is contemplated for the present invention to maintain aphysiologic rate.

Pacing Elements

In a standard dual chamber pacemaker, pacing of both atrium andventricle is possible. In the current invention, pacing of the variouselements will take place once requested by the sensing algorithm. Thestandard burst generator pacemaker employs appropriate technology forthe generation of stimulation pulses in the form of individual pulses orpulse trains having an amplitude up to 7 V and a pulse width of up to 1msec. Most pacemakers have these parameters as a programmable option.The pacing rate is also programmable in most pacemakers and the range isbetween 35-160 beats/min.

Given that the circuitry for pulse generation has become well known tothose skilled in the art, no detailed disclosure is included herein.Specific timing, amplitude, duration and the number of pulses iscontrolled by a microprocessor via data bus under the control of aprogram stored in memory.

Implantable Cardiac Defibrillators

Implantable cardiac defibrillators have significantly reduced the riskof sudden death following hospital discharge, but arrhythmia risk andassociated mortality remains an important problem. Buxton et al.,Current Approaches To Evaluation And Management Of Patients WithVentricular Arrhythmias, Med Health R I, 84(2):58-62 (2001) Arrhythmiasare known to occur in patients having congestive heart failure, atrialfibrillation, ventricular tachyarrhythmias, and bradyarrhythmias. Atrialfibrillation, in particular, is treatable with rate controlanticoagulation or cardioversion followed by maintenance of sinusrhythm. In patients surviving malignant ventricular arrhythmias,however, implanted cardiac defibrillators are especially beneficial.Specifically, in patients with coronary artery disease, decreasedejection fraction, with or without nonsustained ventricular tachycardia,defibrillator implantation can improve survival. Lampert et al.,Management Of Arrhythmias, Clin Geriatr Med, 16(3):593-618 (2000)

Identifying the mechanism of an arrhythmia based on intracardiacelectrograms has become a challenge in the clinical use of implantablecardiac defibrillators. Implantable cardiac defibrillators are primarilydesigned to deliver therapy for life-threatening ventricular arrhythmiasbut frequently deliver inappropriate shocks during supraventriculartachycardias. Tanaka S., An Overview Of Fifth-Generation ImplantableCardioverter Defibrillator, Ann Thorac Cardiovasc Surg., 4:303-311(1998); Thompson et al., supra; Gold et al., A New DefibrillatorDiscrimination Algorithm Utilizing Electrogram Morphology Analysis,Pacing Clin Electrophysiol. 1999;22:179-182 (1999); Barold et al.,Prospective Evaluation Of New And Old Criteria To Discriminate BetweenSupraventricular And Ventricular Tachycardia In ImplantableDefibrillators, Pacing Clin Electrophysiol., 21:1347-1355 (1998); andSchaumann et al., Enhanced Detection Criteria In ImplantableCardioverter-Defibrillator To Avoid Inappropriate Therapy, Am JCardiol., 78:42-50 (1996)

A Dual Chamber Pacing/Sensing Device

FIG. 1 provides one possible embodiment contemplated by the presentinvention; for example, an implantable cardiac defibrillator 13 attachedto pacemaker 14. One of skill in the art will easily recognize that thescope of the present invention is not limited by the device hereindescribed. In fact, many possible engineering designs are compatiblewith the embodiments described herein. It is not intended, therefore, tolimit the present invention to the device depicted in FIG. 1.

The pacemaker/defibrillator is implanted in a surgically-formed pocketin the flesh of the patient's chest 10, or other desired location of thebody. Signal generator 14 is conventional and incorporates electroniccomponents for performing signal analysis and processing, waveformgeneration, data storage, control and other functions, power supply 40(battery or battery pack), which are housed in a metal case (can) 15compatible with the tissue and fluids of the body (i.e., biocompatible).The device is microprocessor-based with substantial memory, logic andother components to provide the processing, evaluation and otherfunctions necessary to determine, select and deliver appropriate therapyincluding electrical defibrillation and pulses of different energylevels and timing for ventricular defibrillation, cardioversion, andpacing to the patient's heart 16 in response to ventricular arrhythmiaand supraventricular tachycardia.

Composite electrical lead 18 which includes separate leads 22 and 27with distally located electrodes is coupled at the proximal end tosignal generator 14 through an electrical connector 20 in the header ofcase 15. Preferably, case 15 is also employed as an electrode such aselectrical ground, for unipolar sensing, pacing or defibrillation.Unlike the defibrillator devices used in previous methods, the signalgenerator and lead(s) of the present invention may be implemented foratrial and ventricular sensing, pacing and defibrillation.Defibrillating shocks of appropriate energy level may be applied betweenthe case and electrode 21 on lead 22 implanted in the right atrium 24through the superior vena cava 31, or between the case and electrode 26on lead 27 implanted through the superior vena cava in the rightventricle 29. Leads 22 and 27 and their associated distal tip electrode32 (to a separate conductor) and distal tip electrode 35 (also to aseparate conductor within the lead), respectively, may be used for botha sensing lead and a pacing lead in conjunction with the circuitry ofsignal generator 14. One of skill in the art may easily recognize thatseparate sensing and pacing leads are also compatible with thisdescribed system. To that end, electrode 32 is positioned in the rightatrium against either the lateral or anterior atrial wall thereof, andelectrode 35 is positioned in the right ventricle at the apex thereof.

Active or passive fixation of the electrodes may be used to assuresuitable excitation. Tip electrode tip 35 preferably has a standard 4 to8 millimeter (mm) configuration, and is provided with soft barbs (tines)to stabilize its position in the ventricle. Each of the electrodes,those used for defibrillation and cardioversion, as well as those usedfor sensing and for pacing, are electrically connected to separateconductors in leads 22 and 27.

If desired, rather than simply using metal case 15 as an electrode, aconductive pouch 37 comprised of a braided multiplicity of carbon fine,individual, predominantly isotropic wires such as described in U.S. Pat.No. 5,143,089 (herein incorporated by reference) is configured toreceive, partly enclose and maintain firm electrical contact with thecase. This serves to enhance the effectiveness of the anodal electrodeof the case and establish a better vector for the electric fieldproduced by the defibrillation shock waveform, and thereby lower thedefibrillation threshold. The conductive pouch can be electricallyconnected directly to an extension lead 38 composed of similar carbonbraid of about 7 french diameter which is implanted subcutaneously forconnection to an epicardial or pericardial patch electrode (not shown)or as a wire electrode (as shown) through an opening formed by puncturesurgery at 39. The conductor for electrode 36 of lead 38 may beimplanted subcutaneously to a point 39, and then by puncture surgerythrough the thoracic cage and the pericardial sac, under a localanesthetic. The lead 38 is run parallel to the sternum, through thepuncture, and then through the patient's thoracic cage and into thepericardial sac. It may even be threaded through the thoracic cage, thepericardial space about the left ventricle and atrium, and back alongthe right atrial appendage, external to the heart. The distal end 36 oflead 38 is preferably placed close to the left atrium of the patient'sheart to provide an increase in electric field strength and support thestrong vector of the electric field according to the heart chamber to bedefibrillated. Selection of the chamber (i.e., atrium or ventricle)which is to undergo defibrillation is made by choosing the appropriateendocardial counter-electrode (21 or 26, respectively) to be energizedtogether with the carbon electrode, if the case 15 or conductive pouch37 is not used directly as the other electrode.

Fabricating the electrode portion of conductor 38 (from the point ofentry 39 into the thoracic cage) of carbon braid provides the desirablefeatures described earlier herein. Proper intracardiac positioningimproves the vector for defibrillation through the atrium as well as theventricle.

Atrial coil electrode 21 is used for bipolar sensing as well as acounter-electrode for defibrillation. Hence, electrode 21 is preferablyalso composed of a braided carbon fiber material described in the '089patent, to take advantage of its very low polarization and lowdefibrillation threshold, to allow the intrinsic rhythm to be detectedalmost immediately after delivery of a shock for accurate determinationof the current status of electrical activity of the atrium. The featuresof low polarization and accurate sensing are important for detection andevaluation of atrial status since atrial signals have magnitudes of onlyabout 20% to 25% those of ventricular signals because of the smalleratrial mass. The braided carbon fiber structure of electrode 21 is alsodesirable to provide a large effective electrical surface area (forexample, in a range from three to six square centimeters) relative toits considerably smaller geometric area, which provides greater energyefficiency-for defibrillation.

As with atrial electrode 21, ventricular electrode 26 of lead 27 ispositioned for use as a defibrillation electrode as well as for bipolarsensing in the ventricle. For defibrillation, electrode 26 alsocooperates with the metal case 15, pouch electrode 37, or pericardialelectrode 36, whichever of these latter electrodes is used in thedefibrillator implementation. Again, a braided conductive structure forelectrode 26 provides it with an effective surface area considerablylarger than its actual exposed surface area. As an alternative, theelectrode may be composed of fine metallic filaments and fibers ofplatinum iridium alloy, braided together to offer similarly desirableelectrode characteristics.

Thus, the tip electrodes of leads 22 and 27 are used for sensing andpacing of the respective atrial and ventricular chambers as in aconventional pacemaker, with dual-chamber pacing, dual-chamber sensing,and both triggered and inhibited response. Further, the defibrillator 13uses a transvenous electrode for ventricular defibrillation andstimulation and an atrial bipolar lead for sensing and atrialdefibrillation, so that atrial defibrillation is performed with one ofthe same electrodes used for atrial stimulation and sensing.

Rather than terminating at distal tip electrode 32, the latter electrodemay be positioned at mid-lead of the atrial transvenous lead 22 whichextends and is threaded through right atrium, ventricle, pulmonaryvalve, and into the left pulmonary artery, with a coil counter-electrode42 connected to a separate conductor of the lead. With this alternativeembodiment, a defibrillating waveform can be applied between electrode42 and atrial defibrillation electrode 21 upon detection of atrialfibrillation. In that configuration, electrode 42 would replace signalgenerator case 15, conductive pouch 37, or lead portion 36 as theselected electrode, and enables a strong vector for the electric fieldthrough right and left atrium. Rather than placement in the leftpulmonary artery, electrode 42 may be positioned in the distal coronarysinus for defibrillation of the atrium in conjunction with electrode 21.

Defibrillation of the atrium and ventricle is achieved by application ofdefibrillation waveforms of suitable shape and energy content betweenappropriate electrodes, such as electrode 36 and electrode 21 for atrialfibrillation, or between electrode 42 and electrode 21 for atrialfibrillation; or between electrode 36 and electrode 26 for ventricularfibrillation, in which atrial electrode 21 can be used additionally aseither anode or cathode. The case 15 can serve as the anode for deliveryof the shock as well, and can provide ground reference potential forunipolar sensing and pacing, in both chambers.

Data Collection

One embodiment of the present invention contemplates an implantablecardiac defibrillator (ICD) that differentiates between supraventriculartachycardia and ventricular arrhythmia based on whether the atria orventricles initiate an electrical signal first following a cessation ofanti-tachycardia pacing.

FIG. 2 demonstrates how one embodiment of the present inventiondiscriminates between one of three situations below that might bepresent during abnormal tachycardia:

-   -   1. The ventricular electrical activity is sensed prior to the        atrial electrical activity: The arrhythmia is originating from        the ventricles and, therefore, defibrillation is required.    -   2. The ventricular electrical activity is sensed after the        atrial electrical activity: The arrhythmia is originating from        the atria and, therefore, defibrillation is not required.    -   3. The ventricular electrical activity is sensed almost        simultaneously with the atrial electrical activity: This        scenario is compatible with a special form of supraventricular        tachycardia known as atrioventricular nodal reentrant        tachycardia which originates from the junction between the atria        and the ventricles and depolarizes these cardiac chambers almost        simultaneously. This form of supraventricular tachycardia is not        life-threatening and therefore defibrillation is inhibited in        this situation.

One embodiment of the present invention contemplates an ICD thatresponds to tachycardia by delivering simultaneous anti-tachycardiapacing bursts (ie., for example, for a period of, but not limited to, 10heart beats) to both the atria and ventricles at a cycle lengthapproximately equal to, but not limited to, 80% of the cycle length ofthe tachycardia. Preferably, the cycle length is modified by alteringthe ICD programning. In one embodiment, tachycardia is terminatedsubsequent to the delivery of the anti-tachycardia pacing burst andobviates the need for an immediate origin diagnosis and defibrillation.Preferably, following tachycardia termination the ICD continues toreceive EGM activity from both the ventricular and atrial sensing leads.In another embodiment, the ICD maintains storage capability such thatall electrical activity sensed from the ventricles and atria areaccessible for downloading for later diagnosis of tachycardial eventsnot requiring defibrillation. In another embodiment, tachycardia is notterminated subsequent to the delivery of the anti-tachycardia pacingburst and the ICD then determines whether the atrial channel or theventricular channel recorded the first electrical activity after ablanking period (i.e., for example, for a length of, but not limited to,200 msec) following the anti-tachycardia pacing burst. Preferably, theblanking period is modified by altering the ICD programming. In apreferred embodiment, the ICD does not defibrillate if the first sensedelectrical activity is atrial (Le., diagnosed as a supraventriculartachycardia). In another preferred embodiment, the ICD does defibrillateif the first sensed electrical activity is ventricular (i.e., diagnosedas a ventricular arrhythmia). In one embodiment, the ICD does notdefibrillate upon an almost simultaneous sensing of electrical activityfrom both the atria and ventricle, wherein said simultaneous electricalactivity occurs within, but not limited to, a 60 msec timeframe (i.e.,diagnosed as an atrioventricular nodal reentrant tachycardia).

In another embodiment, simultaneous anti-tachycardia pacing bursts tothe atria and ventricles controlled by catheter-inserted quadripoleelectrodes results in a termination of the existing tachycardiaarrhythmia. FIG. 3 depicts the last three pacing square wave beats of350 msec duration from an anti-tachycardia pacing burst (STIM), wherethe atrial activation (HRA d and HRA p) is clearly simultaneous withboth ventricle activation OVA p) and His bundle activation (HIS-p, n &d). Following the cessation of the ATP, a normal P-Q-R-S-T profile isvisible (arrow) on the HRA p lead, thus indicating a return to normalsinus rhythm.

In another embodiment, simultaneous anti-tachycardia pacing bursts tothe atria and ventricles identifies the ventricles as originating thetachycardial event. FIG. 4A shows the last three pacing beats induced bya burst of 400 msec square wave depolarizations (STIM triggering ablanking period (blanking period from last ATP stimulation to dashedvertical line). After the blanking period, ventricular activity isrecorded (see RVA d; arrow) prior to atrial activity (see MAP d; arrow).Similarly, FIG. 4B also shows first arriving ventricular activity exceptthat the pacing beats were induced by 350 msec stimulus (STIM) andatrial activation is recorded on HRA d (see arrow) and HRA p leads andcompared with ventricular data recorded on RVA p and RVA d leads (seearrows). Ventricular tachycardia is diagnosed as persistent in bothtracings because the ventricular electrical signal appears prior to theatrial electrical signal during the blanking period.

In another embodiment, simultaneous anti-tachycardia pacing bursts tothe atria and ventricles identifies the atria as originating thetachycardial event. FIG. 5 shows the last two pacing beats induced by a350 msec stimulus (STIM) triggering a blanking period (blanking periodfrom last ATP stimulation to dashed vertical line). After the blankingperiod, atrial activity is recorded (see HRA d or HRA p; arrows) priorto ventricular activity (RVA p or RVA d; arrow). Supraventriculartachycardia is diagnosed as persistent because the atria electricalsignal appears prior to the ventricular electrical signal during theblanking period.

In another embodiment, simultaneous anti-tachycardia pacing bursts tothe atria and ventricles identifies the junction between the atria andventricles as originating the tachycardia event. FIG. 6 shows the lastfour pacing beats induced by a 360 msec stimulus (STIM) triggering ablanking period (blanking period from last ATP stimulation to dashedvertical line). After the blanking period, atrial activity (HRA d),ventricle activity (RVA p) and His bundle activity (HIS d) all appearsimultaneously. Atrioventricular nodal reentrant tachycardia is,therefore, diagnosed.

Experimental

The following are examples that further illustrate embodimentscontemplated by the present invention. It is not intended that theseexamples provide any limitations on the present invention.

EXAMPLE I Anti-Tachycardia Pacing Responses in Patients ExhibitingSupraventricular Tachycardia And Ventricular Tachycardia

This example provides data collected during an electrophysiologicaltesting study demonstrating the effectiveness of anti-tachycardia pacingbursts in patients exhibiting supraventricular or ventriculartachycardia.

A total of twelve patients (three female and nine male) were testedhaving a mean age of 61±19 years. A summary breakdown of the patients bycharacteristics and response to anti-tachycardia pacing for patients isshown in Table 1 below:

TABLE 1 Summary Patient Data For Electrophysiological Testing Study SVTVT Number of Patients 8 4 Age (years) 59 ± 21 65 ± 16 % Female 37 0 LeftVentricular Ejection 52 ± 11  32 ± 10* Fraction (%) % Having CardiacDisease None 75 0 CAD 25 100 Reason For Electrophysiological Study SVT 40 VT 0 4 Other (syncope, 4 0 palpitation etc) Number of ATP bursts per6.0 ± 4.1 8.7 ± 4.7 patient % Termination per patient 44 ± 33 17 ± 22 *p< 0.02

The combined average left ventricular ejection fraction was 45±14% butthere was a significant difference between the eight patients diagnosedas having supraventricular tachycardia (SVT: 52±11%) versus the fourpatients diagnosed as having ventricular tachycardia (VT: 32±10%). Ofthe four ventricular tachycardia patients all had a previous history ofcardiac disease. However, only two of the eight supraventriculartachycardia patients reported any previous history of cardiac disease.The remaining four of the supraventricular tachycardia patientspresented with symptoms such as syncope or palpitations.

Patients were tested in the fasting state and under conscious sedation(0.5-2 mg Midazolam). Lidocaine (1%) was used for local anesthesia whilevenous sheaths (6 Fr or 7 Fr) were inserted into the femoral veins.Quadripolar (5 mm inter-electrode distance and 1.5 mm electrodethickness) were inserted into the venous sheaths and coursed into thehigh right atrial, His bundle and right ventricular apical positionsthat were verified by fluoroscopy observation.

Comparisons of continuous variables between groups was performed usingthe Student t-test. Discrete variables were compared using Fisher'sexact test. A p value<0.05 was considered to be statisticallysignificant.

Catheters were connected to a recording system and a stimulator (EPMedSystem, NY) via a junction box. If an arrhythmia was induced during thecourse of the electrophysiologic study and the patient remainedhemodynamically stable, then attempts at terminating the arrhythmiausing anti-tachycardia pacing (ATP) bursts was performed. The ATP burstswere delivered from the external stimulator by simultaneous pacing ofthe atrium and ventricle at a rate corresponding to approximately 80% ofthe arrhythmia cycle length. The response of the arrhythmia to ATP wasthen recorded. ATP bursting continued until the arrhythmia terminated orthe patient became hemodynamically unstable, at which time thearrhythmia was terminated by external cardioversion (i.e., fall-bodyelectroshock).

The arrhythmia were classified as ventricular (VT) or supraventricular(SVT) by the attending electrophysiologist based on guidelines wellknown in the art. Analysis of the response of the arrhythmia to ATPbursting was noted, as well as the earliest electrical recording (i.e.,whether recorded on atrial sensing leads or ventricular sensing leads).Responses were classified in one of the following categories:

-   -   1. Termination of Arrhythmia: This response is exemplified in        FIG. 3. No further electrogram (EGM) activity analysis was        performed.    -   2. Ventricular Tachycardia Persistence: This response is        exemplified in FIGS. 4A and 4B. During the blanking period, the        earliest EGM activity was recorded by the ventricular sensing        leads.    -   3. Supraventricular Tachycardia Persistence: This response is        exemplified in FIG. 5. During the blanking period, the earliest        EGM activity was recorded by the atrial sensing leads.    -   4. Atrioventricular Nodal Reentrant Tachycardia Persistence:        This response is exemplified in FIG. 6. During the blanking        period, the earliest EGM activity was simultaneously recorded        (i.e., within 50-60 msec) on both the atrial and ventricular        sensing leads. However, for the purposes of the present example        only, this condition was diagnosed as a supraventricular        tachycardia arrhythmia.

Anti-tachycardia pacing bursts were initiated a total of eight-threetimes between the twelve patients. The SVT group experienced forty-eightpacing bursts (6.0±4.1 per patient) while VT group experiencedthirty-five pacing bursts (8.7±4.7 per patient). Following twenty-two ofthe anti-tachycardia pacing bursts, the tachycardia was terminated,while the tachycardia persisted following the remaining sixty-onebursts. The computer algorithm correctly discriminated the firstarriving cardiac electrical signal in all sixty-one of the persistingtachycardias and properly diagnosed twenty-nine persisting tachycardiasas supraventricular and thirty-two persisting tachycardias asventricular.

As such, this protocol results in a 100% sensitivity and a 100%specificity and demonstrates one example of a capability of detecting afirst arriving electrical signal that discriminates extremely wellbetween ventricular and supraventricular tachycardias.

EXAMPLE II Anti-Tachycardia Pacing in an Experimental Mouse Model

This example demonstrates that the mouse may be utilized as anexperimental model to study earliest arriving electrical activitiesfollowing anti-tachycardia pacing to identify the source of cardiactachycardia.

Female FVB mice were anesthetized with xylazine and ketamine (IP)coadminstered with propranolol to reduce the intrinsic heart rate. Undera Nikkon surgical microscope, a 1.7 French octapolar catheter (NuMedInc., Hopkinton, N.Y.) was introduced through the right jugular veincoursing into the right atrium and right ventricle of the mouse. Theelectrode spacing on the catheter tip is 0.5 mm and the electrodethickness is 0.5 mm. A six lead surface electrogram was obtained fromthe mouse by placing one subcutaneous electrode into each limb of themouse, for a total of four. The surface electrograms were filtered at0.01 Hz to 100 Hz, and intracardiac signals sampled at 1 KHz, amplifiedand filtered at 30 to 500 Hz (Labsystem Duo Bard Electrophysiology,Lowell, Mass.).

Demand pacing was achieved by using a single chamber Preva SR pacemaker(Medtronics Inc., Minneapolis, Minn.) set to pace at a very fast rate(up to 400 beats per minute) in temporary mode. The bipolar output ofthe pacemaker was connected by alligator clips to the proximal pins ofthe intracardiac catheter for atrial pacing and the distal pins forventricular pacing. The catheter was also connected to a an externalstimulator (Bloom Associates Ltd., Reading, Pa.) configured to pacesimultaneously the atria and ventricles of the mouse thorough theproximal and distal pins, respectively.

The proper placement of the catheter was verified by the collection ananalysis of a normal sinus rhythm. FIG. 7 illustrates a mouse ECG havinga normal P-Q-R-S pattern on the surface channel (Lead I) at a cardiaccycle length of approximately 180-200 msec (320-300 beats per minute).Note that on the intracardiac channels (see, for example, IC5), the Aand V electrograms correspond to the P and QRS complexes on the surfaceelectrogram, respectively. Specifically, note that atrial EGM activity(A) occurs prior to ventricular EGM activity (V), as expected in sinusrhythm.

FIG. 8 illustrates atrial pacing stimuli (S) at a cycle length of180-200 msec (approximately 320-300) beats per minute to simulate asupraventricular tachycardia. The vertical black lines indicate thepacing stimulus (S) followed by the atrial EGM (A) and the ventricularEGM (V), annotated in Lead IC3. Similar to the normal sinus rhythm datashown in FIG. 7, Lead IC3 of FIG. 8 shows the normal electrocardiogramsequence, with atrial EGM activity (A) occurring prior to ventricularEGM activity (V). Also, the surface P-Q-R-S complex (Lead I) is similarto that of the normal sinus rhythm tracing seen in FIG. 7.

FIG. 9 shows ventricular pacing stimuli (S) at a cycle length of 160-180msec (approximately 375-320 beats per minute), to simulate ventriculartachycardia. The vertical black lines indicate the pacing stimulus (S)followed by the P-Q-R-S response pattern, annotated in Lead IC7.Contrary to the above data in FIGS. 7 and 8, Lead IC7 of FIG. 9 shows areversal of the usual P-Q-R-S complex. Specifically, ventricular EGMactivity (V) occurs first, followed by atrial EGM activity (A). Also,note that the surface P-Q-R-S pattern (Lead I) during ventricular pacingis different than during sinus rhythm and atrial pacing (see FIGS. 7 &8, respectively).

FIG. 10 shows an exemplary tracing of the earliest arriving electricalactivity after ATP on the atrial channel following at least onesimultaneous atrial and ventricular anti-tachycardia pacing (ATP) burstof up to 12 beats per burst with a cycle length of 150-160 msec(approximately 400-375 beats per minute). During simultaneousatrioventricular ATP bursting, the pacemaker output simulating thesupraventricular tachycardia was inhibited. After the last beat ofsimultaneous atrioventricular ATP (Lead IC3; Sa+v: arrow), and anapproximate 75-100 msec blanking period, the earliest electricalactivity recorded was atrial EGM activity (A). Note that pacemakerstimulus (S) resumed following the cessation of ATP bursting and priorto the first arriving atrial EGM activity.

In summary, sixty-nine ATP bursts were delivered in two mice, forty-fiveduring atrial pacing and twenty-four during ventricular pacing. Theearliest electrical activity after ATP was detected on the atrialchannel in all forty-five atrial pacing attempts. Similarly, theearliest electrical activity after ATP was detected on the ventricularchannel in all twenty-four ventricle pacing attempts.

As such, this protocol results in a 100% sensitivity and a 100%specificity and demonstrates one capability of detecting a firstarriving electrical signal that discriminates extremely well betweenventricular and supraventricular tachycardias.

1. An implantable cardiac defibrillator device, comprising: a) animplantable pacemaker, wherein said pacemaker is configured to generatesimultaneous anti-tachycardia pacing bursts such that said pacing burstsgenerate a blanking period; b)an atrial lead and a ventricular leadattached to said device, said atrial lead and said ventricular leadfurther comprising distal tip electrodes configured to deliver saidsimultaneous anti-tachycardia pacing bursts and detect an earliestarriving electrical signal and wherein said implantable cardiacdefibrillator device is configured to determine said earliest arrivingelectrical signal following said blanking period wherein said earliestarriving electrical signal diagnoses an origin of an arrhythmia; and c)a timing device connected to said pacemaker, said timing deviceconfigured to identify that said diagnosed origin of an arrhythmia isselected from between a supraventricular tachycardia, a ventriculartachycardia, and an atrioventricular nodal reentrant tachycardia,wherein said identification of said diagnosed origin of an arrhythmia isbased upon said determination of said earliest arriving electricalsignal.
 2. The device of claim 1, wherein said pacemaker furthercomprises a microprocessor configured to initiate said pacing burst. 3.The device of claim 1, wherein said atrial lead and said ventricularlead further comprise defibrillation electrodes.
 4. The device of claim3, wherein at least one of said defibrillation electrodes is configuredto convert an abnormal heart rhythm into normal sinus rhythm.
 5. Thedevice of claim 1, wherein said pacemaker further comprises a storagememory connected to said atrial and ventricular leads.
 6. The device ofclaim 1, wherein said atrial lead and said ventricular lead arequadripolar.
 7. The method of claim 1, wherein said atrial lead and saidventricular lead further comprise separate conductors.
 8. An implantablecardiac defibrillator device, comprising: a) an implantable pacemaker,wherein said pacemaker is configured to generate simultaneousanti-tachycardia pacing bursts such that said pacing bursts generate ablanking period; b) at least one atrial lead and at least oneventricular lead attached to said device, said at least one atrial leadand said at least one ventricular lead further comprising distal tipelectrodes configured to deliver said simultaneous anti-tachycardiapacing bursts and wherein said implantable cardiac defibrillator deviceis configured to determine an earliest arriving electrical signalfollowing said blanking period, wherein said earliest arrivingelectrical signal diagnoses an origin of an arrhythmia; and c) a timingdevice connected to said pacemaker, said timing device configured toidentify that said diagnosed origin of an arrhythmia is selected frombetween a supraventricular tachycardia, a ventricular tachycardia and anatrioventricular nodal reentrant tachycardia, wherein saididentification of said diagnosed origin of an arrhythmia is based uponsaid determination of said earliest arriving electrical signal.
 9. Thedevice of claim 8, wherein said pacemaker further comprises amicroprocessor configured to initiate said pacing burst.
 10. The deviceof claim 8, wherein said at least one atrial lead and said at least oneventricular lead further comprise defibrillation electrodes.
 11. Thedevice of claim 8, wherein said pacemaker further comprises a storagememory connected to said atrial and ventricular leads.
 12. The device ofclaim 8, wherein said at least one atrial lead and said at least oneventricular lead are quadripolar.
 13. The method of claim 8, whereinsaid at least one atrial lead and said at least one ventricular leadfurther comprise separate conductors.